It is known to use a goniometer to generate, from a constant frequency sinusoidal input signal, a sinusoidal output signal having the same frequency as the input signal but with its phase shifted by a controlled amount with respect to the input signal.
There are two principal types of goniometer, one of which is the capacitive goniometer. One form of capacitive goniometer is disclosed in U.S. Pat. No. 3,264,554 of Hayner et al. In that goniometer, a stator carries four mutually insulated quadrant plates which are supplied with a sinusoidal reference signal, and the connections to the quadrant plates are phased 90 deg. apart. Surrounding the four quadrant plates, and insulated therefrom, is an annular output plate. A rotor which carries a cardioid plate is mounted to rotate about an axis entending through the center of the stator. The cardioid plate is arranged in confronting relationship with the quadrant plates. Surrounding the cardioid plate is a conductive ring which is in confronting relationship with the output ring.
The configuration of the cardioid plate is such that, for any given angular position of the rotor, the cardioid plate is capacitively coupled to at least one of the four quadrant plates. The signals that are coupled to the cardioid plate are additively combined in the cardioid plate and are capacitively coupled to the output ring to provide an output signal which is of the same frequency as the reference signal and has a phase which is dependent on the angular position of the rotor.
The goniometer described in U.S. Pat. No. 3,264,554 is a bulky device, being constructed as the readout device for a magnetic compass. This being so, the rotor and stator are quite large. In addition, an oil dielectric is present between the rotor and the stator. Accordingly, the capacitances of the capacitors are quite large and therefore interference between the reference signal and the output signal does not present a problem. Moreover, the stray capacitance between the quadrant plates and the annular output plate, which depends on the radius of curvature of the quadrant plates, is not substantial in relation to the capacitances of the capacitors and therefore its effect does not reduce substantially the amplitude of the output signal. The goniometer disclosed in U.S. Pat. No. 3,264,554 is not suitable for use in a portable TV vectorscope, to change the phase of the demodulator reference signal, and thereby rotate the vector display, because of its large size. It could not be simply scaled down in size because the reduced distances between components would give rise to excessive interference between the reference signal and the output signal.